1. Field of the Invention
The present invention generally relates to a toner supply device to be used in an image forming apparatus such as a copier, a printer, a facsimile machine, a multi-functional peripheral and the like, and an image forming apparatus including the toner supply device.
2. Description of the Related Art
There have been known various image forming apparatuses including a toner supply device that supplies toner to a development device, the toner contained in an exchangeable toner container, the development device visualizing a latent image to be a toner image, the latent image formed on a surface of a photosensitive drum or the like serving as a latent image carrier.
Among these, there has been known an image forming apparatus including a toner supply device supplying toner to the development device based on the toner consumption in the development device which may be known as a two-component development device using developer including toner and carrier.
Further, as an exchangeable toner container for containing toner, toner cartridges having various shapes are known. For example, some toner cartridges includes a toner bottle having a cylindrical shape. Further, in most of the image forming apparatuses having an exchangeable toner container, to supply the toner to the development device, a feeding screw provided in the cartridge or free fall due to gravity is typically used.
Recently, some image forming apparatuses include a toner storage unit (hereinafter referred to as a “sub-hopper”) inside the main body of the image forming apparatuses, so that toner is supplied from the toner cartridge to the sub-hopper and then the toner is further supplied from the sub-hopper to the development device. For example, Japanese Patent No. 4006215 (Patent Document 1) discloses a configuration including plural toner containing sections in the sub-hopper.
By having this configuration, toner is supplied from the toner cartridge to the sub-hopper and further supplied to the development device via plural toner containing sections of the sub-hopper, using feeding screws serving as feeding members and provided in the respective toner containing sections.
Further, the sub-hopper described in Patent Document 1 includes upper and lower parts. Further, the upper part of the sub-hopper includes two toner containing sections arranged side by side having respective feeding screws in a manner such that the heights of the rotational axes are substantially the same as each other.
On the other hand, the lower part of the sub-hopper includes one toner containing section. Between the two toner containing sections of the upper part of the sub-hopper, there is a dividing plate having openings on the respective ends portions of the dividing plate. By the dividing plate, the two toner containing sections are divided as two sections, which are a toner containing section on the upstream side in a toner feeding direction (hereinafter “upstream-side toner containing section”) and a toner containing section on the downstream side in the toner feeding direction (hereinafter “downstream-side toner containing section”).
An inlet port to receive toner is formed on the upper part on the upstream side of the upstream-side toner containing section. On the other hand, a communication port through which the toner drops to one end part of the toner containing part of the lower part of the sub-hopper (hereinafter “lower toner containing section”) is formed on the downstream side of the downstream-side toner containing section.
By having the configuration described above, toner is supplied from the toner cartridge to the upstream-side toner containing section, and screws are rotatably driven so that toner that cannot be dropped to the lower toner containing section can circulate between the upstream-side toner containing section and the downstream-side toner containing section.
Further, toner having been dropped through the communication port of the lower toner containing section to the one end part of the lower toner containing section is fed to the other end part of the lower toner containing section by a rotatably-driven feeding screw. The toner is further fed to the development device via a discharge port formed on the lower end part in the downstream side of the “lower toner containing section.
As described above, by having the sub-hopper in the main body of the image forming apparatus, it becomes possible to continue printing using toner in the sub-hopper for a certain time period even when there is no toner remaining in the toner cartridge that is to be exchanged by the user. Namely, even when there is no toner remaining in the toner cartridge and it is required to exchange the toner cartridge, it is possible to delay the exchange of the ink cartridge until the image forming apparatus is not used, which may make great contribution to the reduction of the down time of the image forming apparatus.
Further, it may become possible to make it easier to reduce the size of the image forming apparatus because the structural limitation in the positional relationship between the toner cartridge and the development device due to no sub-hopper is alleviated. Further, when compared with the configuration where ink is directly supplied from the ink cartridge to the development device, it may also make it easier to more accurately supply ink in the configuration in which the sub-hopper is provided in the main body of the image forming apparatus.
Further, in the configuration of Patent Document 1, toner is directly fed from the sub-hopper to the development device through the discharge port formed of the lower toner containing section. However, there has been another method to feed toner from the sub-hopper to the development device. For example, unlike the method in Patent Document 1, there is also a known method in which a feeding member such as a spiral screw or coil is provided in a tube-like feeding path so as to feed toner by the rotation of the spiral screw or the coil.
In the mean time, demands for reducing the size and the cost of the image forming apparatus are getting more and more stronger. However, it may be difficult to meet the demands when the sub-hopper include the upper and the lower parts as described above.